Musannaf Ibn Abi Shaybah 25699 — Drinking from the mouth

It is narrated from Sayyiduna Abu Sa'id (may Allah be pleased with him), who said: A man drank water from the mouth of a waterskin and a snake went into his stomach, so the Messenger of Allah (peace and blessings be upon him) forbade bending back the mouths of waterskins to drink from them.